1. Field of the Invention
The present invention relates to a quantum cascade detector utilizing intersubband light absorption in a quantum well structure.
2. Related Background Art
As a photodetector in the mid-infrared wavelength region, normally, a HgCdTe (MCT) detector is used. However, this MCT detector has a problem such as containing toxic environmental pollution materials, so that the MCT detector cannot be generally and widely used. Therefore, a novel photodetector in such a wavelength region has been demanded.
In recent years, as such a photodetector, quantum cascade detectors (QCD) using GaAs/AlGaAs quantum cascade structures, etc., have been reported. A quantum cascade detector is a photodetector which absorbs light in its cascade structure, and by measuring the amount of current flowed by carriers generated by the light absorption, detects incident light, and is operable with no bias. Further, in the quantum cascade detector, as in the case of a quantum cascade laser, by multistage cascade-coupling semiconductor lamination structures each including an absorption well layer that absorbs light, light can be more efficiently absorbed and detected (refer to Patent Document 1 and Non-Patent Documents 1 and 2).    Patent Document 1: Japanese Patent Application Laid-Open No. 2013-41933    Non-Patent Document 1: F. R. Giorgetta et al., “Quantum Cascade Detectors,” IEEE Journal of Quantum Electronics Vol. 45 (2009) pp. 1039-1052    Non-Patent Document 2: L. Gendron et al., “High resistance narrow band quantum cascade photodetectors,” Appl. Phys. Lett. Vol. 86 (2005) pp. 121116-1-121116-3